This invention relates to nonwoven fabrics and fabric laminates made by thermally bonding fibrous webs formed from certain types of multiconstituent fibers. Thermal bonding of the nonwoven fabrics may be accomplished by calender or "through air" techniques or ultrasonically. The multiconstituent fibrous webs may contain other fibers in addition to the thermoplastic multiconstituent fibers. The nonwoven fabrics and fabric laminates produced according to the present invention may be optimized as to softness and strength characteristics.
Nonwoven fabrics and fabric laminates are widely used in a wide variety of everyday applications, as for example, as components in absorbent products such as disposable diapers, adult incontinence pads and sanitary napkins; in medical applications such as surgical gowns, surgical drapes, sterilization wraps; and in numerous other applications such as disposable wipes, industrial garments, housewrap, carpets and filtration media.
By combining two or more nonwoven fabrics of different types, nonwoven fabric laminates have been developed for a variety of specific end use applications. For example, nonwoven fabric laminates have been developed to serve as a barrier to penetration by liquids or microorganisms. Barrier fabric laminates of this type typically comprise one or more microfibrous (for example meltblown) polymer layers, combined with one or more layers of another type of nonwoven fabric, such as a spunbonded nonwoven fabric. Nonwoven barrier fabrics of this general type are used as medical and industrial garments, CSR wrap, surgical drape and housewrap. Specific examples of such fabrics are described in U.S. Pat. Nos. 3,676,242, 3,795,771, 4,041,203, 4,766,029 and 4,863,785.
While nonwoven fabrics of this general type have found widespread use in various applications, as noted above, there are many applications in which it would be desirable to have a fabric with improved softness, drape and/or strength characteristics.
The present invention uses certain multiconstituent fibers in the production of nonwoven fabrics and fabric laminates, and has thereby achieved improvements in softness, drape, strength and other characteristics. The multiconstituent fibers are of the random matrix type and are formed by melt extruding a highly dispersed blend of two or more polymers having low affinity for one another.
Various types of random matrix multiconstituent fibers are described in the literature. For example, in some instances blends of different polymers are extruded from the orifices of spinnerets in order to make fibers containing "free form" microfibrils which can then be separated from the matrix polymer. Note for example, Breen U.S. Pat. No. 3,382,305, Twilley U.S. Pat. No. 3,369,057, and Allan (U.S. patent application Ser. No. 07/220,203).
A few references cite fibers and nonwoven fabrics made from polymer blends wherein the dominant continuous phase is lower melting than the dispersed noncontinuous phase; see Kubo (European Patent Application No. 0277707), Wincklhofer U.S. Pat. No. 3,620,892 and Vassilatos U.S. Pat. No. 4,632,861. By definition, to thermally bond such fibers, portions of the continuous fiber phase are raised to temperatures where partial molecular relaxation of the continuous lower melting phase occurs. Relaxation occurs not only at the bond site proper but also in the fiber region surrounding the bond site which is responsible for distributing a load or strain throughout the bonded fiber network. Although thermally-bonded nonwoven fabrics can be made from these materials, strength is compromised.
Published European Application 405,793 describes fibers, films and articles made from a blend of compatible polymers, including a non-crystalline mesomorphous polypropylene and another polymer compatible therewith. Other melt spun fibers formed from polymer blends are described in Brody et al. U.S. Pat. No. 4,822,678, Jezic et al. U.S. Pat. No. 4,839,228 and in Published European Patent Application 416,620.
Finally, Graham U.S. Pat. No. 4,769,279 refers to meltblown fibers and fabrics made from blends of ethylene/acrylic copolymer with a second fiber-forming polymer such as a polyvinyl, a polyamide, and a polyolefin. Graham does not disclose thermally-bonded nonwoven fabrics from engineered fibers, however. Furthermore, the Graham disclosure is limited to blends based upon low viscosity ethylene/acrylic copolymers.